The present invention relates to a structure of a variable resistor in which a rotor with a sliding member is rotatably fixed with respect to a substrate provided with a resistor on the surface thereof.
The variable resistor shown in FIGS. 23 and 24 has been known as an electronic component in which a rotor, a stator and the like are incorporated.
In this variable resistor, reference numeral 150 designates the insulating substrate, and the resistor 151 and the collector electrode 152 are provided on the surface thereof. Reference numerals 161, 162 and 163 designate lead terminals; the terminal 161 is electrically connected to one end of the resistor 151, the terminal 162 to the other end thereof, and the terminal 163 to the collector electrode 152, respectively.
The brush-shaped sliding member 165 is fixed at the substrate portion thereof to the concave recess 170c provided at the under surface of the rotor 170, and moves slidably on the resistor 151 and the collector electrode 152. The drive-engaging groove 170b is formed at the projection 170a of the rotor 170.
The case 180, through the O-ring 190, rotatably mounts the rotor 170 on the substrate 150. The member 165 is secured to the rotor 170, and the case 180 has an opening 180a at its upper surface exposing to the outside the convex projection 170a of the rotor 170. The O-ring 190 is formed of a seal resin which is made of thermosetting epoxy resin or the like and is obtained through potting and curing thereof to keep the inside of the case airtight and at the same time to retain the rotor 170 within the case 180. The O-ring also functions to secure the substrate 150 to the case 180.
In this variable resistor when the rotor 170 is rotated with respect to the substrate 150 and the case 180 using its driver-engaging groove 170b, the sliding member 165 slides on the resistor 151 and the collector electrode 152 with the result that the resistance value between the terminals 162 and 161 or 163 is adjusted.
But, in such a variable resistor as above-described, various problems have been caused, including difficult assembly, by employing the large number of parts such as substrate 150, sliding member 165, rotor 170, case 180 and the like. Also, the growing need for accuracy in mutually positioning components for automatic assembling results in reduced productivity efficiency when a large number of parts must be assembled.
In addition, potting is required for the seal resin 190 in securing the substrate 150 to the case 180, which has been a barrier to automatic assembling of the components due to difficult adjustment of the injection amount of the seal resin. Moreover, it takes substantial time to cure the seal resin 190 and such curing necessitates additional manufacturing equipment. In the seal-type structure case, heat applied to cure the seal resin causes inner pressure to go up within the case, thereby forcing open a hole in the seal resin 190. Accordingly, productivity has not been improved.
Also, in the conventional variable resistor above-described, there are two ways of mounting on the printed substrate, regular 2.5 mm pitch and irregular 2.5 mm pitch, the intervals among the terminals 161, 162 and 163 being different according to the type of mounting. Differences in intervals cause different types of components to be produced with the result that the same shaped dies can not be used for manufacturing the case, the substrate and the terminals. Moreover, as shown in FIGS. 23 and 24, the terminals are projected in two ways; one is from the side of the case 180 and the other from the bottom thereof. Accordingly, it is necessary in the production line to take into consideration the above-described two types of terminal pitches and combinations therewith of different projection directions, thus resulting in complicated control of stored parts and products.
A sliding member is shown in FIG. 25 as one example of use of a conventional variable resistor in which the arm 193 with a cut 192 therein is formed at the periphery of the disk-shaped substrate portion 191. The arm is bent at both ends 193b, 193b thereof with its central part projecting horizontally to define contact portions 193b, 193b. The cut 192 divides contact portions 193b, 193b into two to heighten contact reliability.
But, as shown in FIG. 26, with this sliding member, when the contact portions 193b, 193b are out of contact with the resistor they are in the position shown in a solid line, while when forced to contact it they come to the position shown in a chain line.
In other words, depending on conditions, the contact portions 193b, 193b of this sliding member shift in the radial direction of the sliding member as shown by the arrow D.
The fact that the portions 193b, 193b are in a radially inwardly shifted position, when out of contact with the resistor relative to when in contact therewith, causes difficulty in molding the sliding member at the rotor. When the sliding member is molded at the rotor, the contact portions 193b, 193b, out of contact with the resistor, are housed in the space of a metal mold, and the position shifted to the inside requires a thinned portion in the metal mold which is disadvantageous in processing the mold as well as to its useful life.
In addition, this construction poses a problem in that, since the divided contact portions 193b, 193b are disposed side by side, their movement on the resistor is restricted due to mutual interference thereby, and also miniaturization of the sliding member itself is limited from a constructional viewpoint.
Accordingly, it is proposed that an arm 293 simply be cut at the central part thereof by a straight line M in such a manner as to divide it into two in the peripheral direction and that end portions thus obtained are again bent to define contact portions 293b, 293b as shown in FIG. 27. In this case, the line M tilts with respect to the line A going through the center of the substrate portion 291. But, another problem is created in that contact portions 293b, 293b of this sliding member are small in width thereby causing difficulty in processing and miniaturization thereof.
It is also proposed that, as shown in FIG. 28, an arm 393 is cut at the central part thereof with a straight line N to form contact portions 393b, 393b. The line N in this case intersects the line A at a right angle. While the contact portions 393b, 393b have larger widths in this sliding member, a gap can not be formed between the contact portions 393b, 393b, like those in FIG. 25, thus causing mutual interference therebetween.
In addition, both device shown in FIGS. 27 and 28 have the arms bent at bending points 291a and 391a, respectively, along the lines A' going through the center of the substrates so that, like those shown in FIG. 25, the contact portions move horizontally to the left when not in contact and to the right when in contact, respectively, with respect to the substrate portions, thereby making molding at the rotor difficult.